Filament supply system for vibrator operated receivers



April 5, 1938. P. F. G. HOLST 2,1 1

FILAMENT SUPPLY SYSTEM FOR VIBRATOR OPERATED RECEIVERS Filed March 13, 1936 I l/Vl/E/VF'UE fuzz/5]: 6.570655 HTTOk/VEY.

Patented Apr. 5, 1938 UNITED STATES FI-LAMENT SUPPLY SYSTEM FOR VIBRATOR I OPERATED RECEIVERS Poul F. G. Holst, Oaklyn, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 13, 1936, Serial No. 68,668

- 6 Claims. (01. 250-47) The present invention relates to a filament supply system for a vibrator operated radio receiver, and has, for its object, to provide an improved system whereby quiet operation is obtainable in connection with a vibrator circuit.

As is well known, a vibrator, used in connection with a radio receiver, is an electrical make and. break contact device provided in conjunction with a step-up transformer for changing the 6 volt battery current into high voltage supply current for the anode and screen grid circuits of a radio receiver. Such systems, of whatever character, are known generally as vibrators, and include make and break contacts, which may be the source of interference voltages and of ripple currents which may, if not properly filtered and balanced, appear in the operating circuits of an associated radio receiver, rendering its operation faulty because of the noise picked up from the vibrator circuits.

The invention, therefore, has, for its further object, an improved arrangement of the filament and supply circuits for a radio receiver operating from a storage battery or the like, and having, associated therewith, a vibrator B supply device.

The invention will, however, be better understood when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing,

Fig. l is a schematic circuit diagram of a storage battery operated receiverprovided with a vibrator type of anode current supply means and embodying the invention,

Fig. 2 is a simplified schematic-circuit diagram of the filament circuit per se of the system of Fig. l, and

Fig. 3 is a similar filament circuit showing a modification thereof.

Referring to Fig. l, a series of electric discharge devices or tubes 5, 6, 1, 8, 9 and ID are arranged in a superheterodyne receiver circuit as the detector-oscillator, intermediate frequency amplifier, second detector, audio frequency amplifier or driver, and the output tubes. As indicated in the drawing, the second detector I is of the diode type, and is-provided with a heater type cathode II, the heater of which is indicated atl2. Allof the remaining tubes are of the filament type, the filaments therefor being indicated at [3; It will be noted thatthe filaments of the detector-oscillator intermediate frequency amplifier and audio frequency amplifier tubes 5, B and-8 are connected in parallelacross filament supply leads I4 and: I5, and that the filaments are center-tapped to ground; through a center tap resistor l-I connected between the leads [4 and l5.

Positive potential from the storage battery is applied to the lead l4 through a supply lead l8 connected with the battery I9, and the filaments I 3 of the power output tubes 9 and H) are connected with the lead l5 through a series resistor or R1. The filaments l3 are connected in parallel, and are provided with a parallelor-shunt by-pass resistor 2| or R2 which, in .turn, is connected through a connecting lead 22. with the negative battery supply lead indicated at 23.

The leads 23 and IB fromthe. battery are arranged in a cable as a pair of closely associated leads, as indicated in the drawing, and'are connected through the receiver, as will be seen, through a series filament circuit, more clearly illustrated in Fig. 2, to which attention is. directed along with Fig. 1. In this figure the same reference numerals are applied to the same parts throughout. It will also be noted that the heater l2 for the detector-audio frequency amplifier tube 1 is connected directly. across the supply lines, the connectionsin Fig. 1' being indicated at 24.

The bias supply. potential forthe various tubes may be derived from any suitable source, such as the series filament circuit or from the automatic volume control system provided inconjunction with the second detector I. This circuit includes the detector diodes 25, the intermediate frequency input circuit 26, a filter resistor 21, a diode output impedance 28, and the cathode return lead 29. also provided with'a self bias resistor 30, to which the amplifier grid 3| is connected through a'coupling resistor 32 and filter resistor 33; whereby the grid 3| is self-biased. Rectified signal potentials or audio frequency signals are also applied to the amplifier grid'3l through a tapconnection 34 and a coupling capacitor 35;" with the grid resistor 32, as indicated. Automatic volume control potentials are applied to the detectoroscillator 5 and intermediate frequency amplifier 6 through a lead 31 from the negative supply point 38, and a fixed initial bias is also derived for the grids of the tubes 5 and Gfrom the drop in the series filament circuit between the negative lead and the various filaments thereof, which drop is counteracted by the fixed biased potential derived from the self-bias potential 30. The differential, between the drop through the resistor 30 and the drop through the resistor-R1 or 20, and the cathode of the'outputltubes 9.; and

The cathodeflead 29 is 3 I is suificient to provide a low initial bias on the grids of the tubes 5 and 1, which, it will be seen, is increased in response to signals by the flow of current through the diode output resistor 28, thereby effecting automatic volume control.

The bias potential of the audio frequency amplifier tube 8 is provided between the negative lead 22 and the cathode of the tube 8 which is, in effect, the drop through the filaments of the output tubes and through the resistor R1, proper for negative bias of the first audio frequency amplifier tube. The output tubes 9 and ID are of the zero bias Class B amplifier .type and are operated without negative bias. Therefore, a direct connection is provided between the secondary 40 of the coupling transformer and the oathodes, as indicated at 4|. The problem of filtering this grid circuit, is, therefore, reduced to a minimum. However, it will be noted that the grid circuit for the first audio frequency amplifier 8 is provided with a suitable filter 42 to prevent ripple potentials from reaching the grid, and the cathode lead 29 of the second detector is provided. with a relatively large by-pass capacitor 43 to ground, whereby it is by-passed substantially directly to the center tap on the resistor i7 across the filament leads l4 and I5. This has been found to effectively eliminate hum and ripple voltage effects in the audio frequency amplifier.

The detector-oscillator tube 5 and the intermediate frequency amplifier 6 are connected in parallel with the mid-tap resistor l1 and the capacitors in the grid supply filters are connected to ground. This connection insures a minimum of modulation effects from the ripple voltage across the filament supply.

In this connection the by-pass capacitors 44 should be'substantially equal and operate in the detector-oscillator circuit and in order not to disturb the center tap to ground through the resistor l1 these capacitors must be equal or substantially so.

The ripple is further reduced by connecting the vibrator or B supply device, indicated at 45, with the battery l9 through separate supply leads 46, and further providing the supply leads 46 with a shielded and grounded cable shield indicated at 41. The control switch for the vibrator is indicated at 48, and one side thereof is connected to ground 49 through a by-pass capacitor 50 to which ground also is connected the cable shield 41 through a short lead connecting 5|.

The use of two independent battery cables, one for the vibrator and one for the filament, has been found to prevent a ripple across the vibrator cable from being impressed upon the filaments, and effectively eliminated a disturbance, which heretofore has been difficult to suppress. With this arrangement, the only impedance common to the vibrator supply circuit and the filament circuits is the battery impedance which is relatively low and, by shielding the vibrator supply cable, the filament and vibrator low potential circuits are effectively isolated, resulting in material reduction in the interference noise experienced with storage battery operated vibrator tube receivers in recent production.

Furthermore, the use of a grounded mid-tap for the tubes in the filament circuit most susceptible to disturbances from ripple voltages, such as the first audio frequency amplifier tube, for example, and the use of a heater type audio frequency detector, has further prevented vibrator hum from being impressed upon the filaments of the tubes in which the hum would be most undesirably amplified. It will be seen that the audio frequency detector and first audio frequency amplifier are sensitive to hum voltages since the amplification following is relatively high.

In a series filament circuit comprising a plurality of tubes in a superheterodyne receiver of the type described, the use of a diode second detector with the diode-cathode and the common audio frequency amplifier cathode, by-passed to ground and to the center tap of the audio frequency amplifier filament circuit, the slight remaining hum is reduced for the reason that the by-pass capacitor such as the capacitor 43, in the present example, is a combined by-pass and filament capacitor.

The vibrator output may also be provided with a radio frequency by-pass provided by a choke coil 55 and by-pass capacitor 56 to ground in the positive B supply lead, and the negative B supply lead may be connected to ground as indicated at 51.

v The filament circuit may also be rearranged, as shown in Fig. 3, to provide a center tap resistor such as shown at 20 directly across only the filament l3 of the audio frequency amplifier tube, while the output-tubes are connected separately through resistors 58 and 59 with the audio frequency amplifier and the detector-oscillator tube filaments, as indicated. The intermediate frequency amplifier tube filament is provided also with a series resistor 60, whereby the filaments are separated in groups having substantially the same current ratings.

It will be noted that the detector-oscillator, the intermediate frequency amplifier, and the audio frequency amplifier filaments are all connected to the same lead and center tap resistor as in Figs. 1 and 2, so that, in effect, the center tap on the filament of the audio frequency amplifier tube is the same as before and effective on all of the sensitive tubes.

Both the detector cathode and the filament circuits for the audio frequency amplifier and other filaments in its group are provided with low audio and radio frequency paths to ground or chassis. This is particularly desirable for vibrator ripple currents which are sufficiently high to cause the battery leads to represent relatively high impedance thereto.

I claim as my invention:

1. In a radio receiving system provided with a vibrator B supply device and battery type filament circuit, means for reducing noise in the system,

comprising an audio frequency detector having a heater connected with said circuit, an audio frequeny amplifier having a filament, a series filament circuit including means providing a center tap to ground for said audio frequency amplifier circuit, and a separate pair of supply leads for the vibrator device adapted to be connected with a common battery supply, source with the filament circuit, whereby said circuits are common to each other only through the low impedance of said common battery supply source.

2. In a battery type radio receiving system of the superheterodyne type, the combination with a vibrator B supply device therefor, of a filament supply system including a second detector having a heater typecathode, a series filament circuit for the remainder of the tubes in said receiver including a first audio frequency amplifier, means providing acenter tap ground connection for that portion of the series filament circuit including said first audio frequency amplifier, means providing a self-bias resistor in circuit with the cathode of said second detector and a by-pass capacitor connected between the cathode end of said resistor and the center tap ground connection of said filament circuit.

3. In a battery type radio receiving system of the superheterodyne type, the combination with a vibrator B supply device therefor, of a filament supply system including a second detector having a heater type cathode, a series filament circuit for the remainder of the tubes in said receiver including a first audio frequency amplifier, means providing a center tap ground connection for that portion of the series filament circuit including said first audio frequency amplifier, means providing a self-bias resistor in circuit with the cathode of said second detector and a by-pass capacitor connected between the oathode end of said resistor and the center tap ground connection of said filament circuit, and means providing a zero bias Class B amplifier in the output circuit of said receiver.

4. In a battery type radio receiving system of the superheterodyne type, the combination with a vibrator B supply device therefor, of a filament supply system including a second detector having a heater type cathode, a series filament circuit for the remainder of the tubes in said receiver including a first audio frequency amplifier, means providing a center tap ground connection for that portion of the series filament circuit including said first audio frequency amplifier, means providing a self-bias resistor in circuit with the cathode of said second detector and a by-pass capacitor connected between the cathode end of said resistor and the center tap ground connection of said filament circuit, and means providing separate pairs of supply leads for said vibrator and for said series filament circuit for battery connection, whereby the impedance of the battery alone is common to said vibrator and said filament circuits.

5. In a battery type radio receiving system of the superheterodyne type, the combination with a vibrator B supply device therefor, of a filament supply system including a second detector having a heater type cathode, a series filament circuit for the remainder of the tubes in said receiver including a first audio frequency amplifier, means providing a center tap ground connection for that portion of the series filament circuit including said first audio frequency amplifier, means providing a self-bias resistor in circuit with the cathode of said second detector and a by-pass capacitor connected between the cathode end of said resistor and the center tap ground connection of said filament circuit, means providing a zero bias Class B amplifier in the output circuit of said receiver, and means providing separate pairs of supply leads for said vibrator and for said series filament circuit for battery connection, whereby the impedance of the battery alone is common to said vibrator and said filament circuits.

6. In a radio receiving system provided with a vibrator B supply device and battery type filament circuit, a heater type audio frequency detector, connected with said circuit to receive heater current therefrom, an audio frequency amplifier having a filament, a series filament circuit connected with said first named circuit and including said filament, means providing a center tap ground connection for said amplifier filament, and separate pairs of current supply leads for the series filament circuit and said vibrator, whereby said filament and vibrator supply circuits are common to each other only through the low impedance of a common battery supply source, said second detector having a self-bias resistor in the cathode circuit thereof, and means providing a by-pass capacitor connection to ground from the cathode end of said resistor and from said center tapped filament circuit.

POUL F. G. HOLST. 

